The ultrastructural techniques of electron microscopy (EM), electron histochemistry (EH) and tridimensional reconstruction (TDR) after electron and light microscopy of serially sectioned lung as well as tracer techniques such as the retrograde and orthograde transport of horseradish peroxidase (HRP) will be used to study the sensory and motor innervation in adult lung of several species including human autopsy material. The development of nerves in fetal and newborn lung will also be studied utilizing these techniques. Sensory receptors and neurons which respond to stimuli such as stretch or irritants will be distinguished from motor nerves by their ultrastructural characteristics such as number of mitochondria, myelination, presence of beta glycogen, vesicle size and type, as well as by their three dimensional relations to other pulmonary structures. They will also be identified and traced after application of HRP at several anatomic sites by several experimental procedures. Autonomic nerves will be identified by their histochemical reactions for choline acetyltransferase and acetylcholinesterase, by their vesicle size and type, and by the chemical denervation of sympathetic postganglionic nerves by 6 hydroxydopamine. The three dimensional relationships of parasympathetic nerves in intrapulmonary structures such as mucus glands and airway smooth muscle will be studied. The sympathetic postganglionic nerves will be analyzed similarly especially in the pulmonary vasculature and in the vasa vasora. Many questions revolve about the functional role of the intrapulmonary nerves and their reflexes in normal and diseased lung. In many areas, the morphology can be expected to help answer many physiologic and pathophysiologic questions as well as to aid in the development of specific therapy.